This invention relates generally to a semiconductor integrated circuit device, and more particularly to a technique which is effective when applied to a semiconductor integrated circuit device having a microcomputer function, for example.
In a 1-chip microcomputer, for instance, predetermined data processing is performed in accordance with a program written into its built-in read-only memory (ROM). If the circuit arrangement is such as to output the programmed data of this built-in ROM to an external terminal, the possibility exists that the content of the program will be known to a third party. This is undesirable from the aspect of protection of software. However, the program content must be read out to the external terminal in order to test the memory.
As one prior art reference relating to the 1-chip microcomputer, mention can be made of the "Hitachi Microcomputer Data Book, 8-Bit Single Chip" published by Hitachi, Ltc., September, 1983, which is hereby incorporated by reference.